As it happens May 4 has been a significant date for several social justice movements led by students.
On May 4, 1919 a large demonstration in Beijing protested against the treatment of China in the Versailles treaty. The movement that this was a part of became known as the May 4 Movement. It was largely led by students who supported a broad liberalization of their society. They wanted to adopt western values of democracy and an end to the strict class divisions of traditional Chinese society. They supported literature in the vernacular language of the the people, rather than just being for the intellectual class. Politically they opposed foreign domination of China and thought that by adopting western values, China could become a self-reliant nation that could control its own destiny. This movement was very influential among intellectuals and students who later went on to reshape Chinese society.
On May 4, 1989 the democracy movement centered around Tienanmen Square in Beijing was building strength and marked the 70th anniversary of the May 4th Movement with a rally that brought out 100,000 people into Tienanmen Square. The Democracy Movement advocated an end to the domination of the Communist Party and the institution on democratic institutions and free speech. The movement paralleled similar movements in other Communist countries that led to the collapse of Communism in the Soviet Union and Eastern Europe. In China, however, the movement was crushed when the military marched on Tienanmen Square on June 4, killing anywhere from several hundred to several thousand people.
On May 4, 1961 in the United States, the first of the Freedom Rides began. Students from around the country came to the South to challenge segregation of interstate transportation. They rode Greyhound and Trailways buses in groups of black and white people riding together and using the facilities at bus stations together in defiance of segregation laws. They were met with mob violence and eventually the governor of Alabama had to call out the National Guard to protect them and to forestall the use of federal troops. These rides were an important milestone for the Civil Rights movement and eventually forced the end of segregation in public transportation.
On May 4, 1970 four students at Kent State University were shot by the Ohio National Guard while protesting the Vietnam War following President Nixon's announcement that he was expanding the war into Cambodia. Their deaths and the death of two more students at Jackson State in Mississippi the night of May 14 sparked a nationwide student strike by as many as 4 millions students and mobilization against the war. Hundreds of universities closed down in the face of the protests. Many students were galvanized into action by the thought that "it could have been me". They were in danger if they were drafted to fight in Vietnam and now they were in danger if they stayed in school. They felt personally threatened and responded with renewed action against the war.